Obituary: Jan Beenakker, 1926-1998

Jan Beenakker passed away on July 23, 1998. A brief illness brought an
unexpected end to fifty years of dedicated service to physics in Leiden and
Dutch science in general.

Jan Beenakker was born in Koog aan de Zaan (North-Holland) on February 1,
1926, as the first child of a railway employee from Leiden. As his family moved
from one train station to another, he grew up first in Zeeland and then in
Rotterdam. There he concluded his high school education at the Saint Francis
Gymnasium (1943), but could not continue with university because of the war.
After the liberation in 1945 he started the study of physics in Leiden. He
would commute from Rotterdam and in that city was an active youth member of the
labor union. After a break for military service (as a meteorologist), his
masters degree in physics followed in 1951 and his Ph.D. in 1954. His thesis
"The influence of the Helium isotope with mass 3 on the properties of liquid
Helium II" was done under the direction of Cor Gorter, the head of the
Kamerlingh Onnes Laboratory in Leiden. (Altough his actual mentor was Krijn
Taconis.) Beenakker stayed at Leiden University until his retirement in 1991,
interrupted only for a sabbatical leave at MIT in 1969/1970. He was promoted to
Reader in 1959 and to full Professor in 1963, and also held a position as
visiting professor at the Catholic University of Leuven (1961-1992).

While the topic of the thesis still followed the Leiden tradition in low
temperature physics, it already contained the seed of what would become
Beenakker's broad interest in thermodynamic and transport properties of
molecular liquids and gases. In the early sixties Jan Beenakker, motivated by
Gorter, entered the field in which he and his group would play a pioneering
role: The transport properties of non-spherical molecules. Using highly
sensitive techniques, measurements were performed of the heat conductivity and
viscosity of molecular gases in a transverse magnetic or electric field. This
led to the discovery of new phenomena that have a certain similarity to the
Hall effect and stimulated extensive theoretical research. It was believed from
early work of Senftleben that an external magnetic field would only influence
paramagnetic molecules such as NO and O2, but Beenakker (working
with his younger colleague Hein Knaap) showed experimentally that it is a
much more general property of non-spherical molecules. Also diamagnetic gases
such as N2 and CH4 are influenced by an external field as
a result of precession between collisions. Such field effects are now known as
Senftleben-Beenakker effects.Here you can read how Jan Beenakker recalled the excitement of his discovery twenty-five years later.

Later Beenakker extended his research to transport properties in the
rarefied gas regime, where boundary layer effects are essential. New phenomena
such as a viscomagnetic heat current and thermomagnetic pressure difference
were observed. For the first time it became possible to measure directly the
nonequilibrium molecular velocity distribution in a heat conducting gas. This
experimental research program was carried out in close collaboration with a
variety of theorists, who would be regular and long-term visitors to Leiden.
The international scientific collaboration culminated in the monumental
monograph "Nonequilibrium Phenomena in Polyatomic Gases" (Clarendon,
Oxford, 1991), which Beenakker co-authored with Fred McCourt (Waterloo), Walter
Köhler (Erlangen), and Ivan Kuscer (Ljubljana).

In parallel to his scientific research, Beenakker contributed to Dutch
science policy at the request of the minister Pais of Science and Education. In
Leiden he served as Dean of the Faculty of Sciences and Rector Magnificus of
the University (1985-1991). More than many of his colleagues, he had a good eye
for the political reality that constrains the desires of the scientific
community. After his retirement he chaired the Dutch Science Foundation FOM,
without losing his interest and involvement in research: He finished the
manuscript of his last paper (with Sergei Krylov) just a few weeks before his
death.

His long-time collaborator and friend Jo Hermans gave the following
characterization of Jan Beenakker as a person: "Jan was modest and a bit shy
and those who did not know him well could find it difficult to make contact.
But he formed unusally close bonds with the members of his group. Not only was
he an inspiring thesis advisor, quick and creative in the scientific debate; He
was also a wise counsel and a father figure in the classic sense of the word:
Generous with praise and honest with criticism. He posessed a highly developed
sense of social responsibility, and would be especially attentive to the needs
of the non-scientific staff. The result of all this was that the
members of the Beenakker group kept strong ties to their teacher long after
they had left Leiden."

Beenakker was a member of the Royal Netherlands Academy of Arts and Sciences and a
Doctor Honoris Causa from the University of Waterloo (Canada). He was knighted
both in the Dutch and Belgian royal orders. Dutch physics in general and Leiden
physics in particular has much for which to thank Jan Beenakker. We will miss
his wisdom.